MAPPING QUANTITATIVE TRAIT LOCI USING MULTIPLE FAMILIES OF LINE CROSSES

To avoid a loss in statistical power as a result of homozygous individ uals being selected as parents of a mapping population, one can use mu ltiple families of line crosses for quantitative trait genetic linkage analysis. Two strategies of combining data are investigated: the fixe d-model and the random-model strate???? gies. The fixed-model approach estimates and tests the average effect of gene substitution for each parent, while the random-model approach treats each effect of gene sub stitution as a random variable and directly estimates and tests the va riance of gene substitution. Extensive Monte Carlo simulations verify that the two strategies perform equally well, although the random mode l is preferable in combining data from a large number of families. Sim ulations also show that there may be an optimal sampling strategy (num ber of families vs. number of individuals per family) in which QTL map ping reaches its maximum power and minimum estimation error. Deviation from the optimal strategy reduces the efficiency of the method.